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Nutplates

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DeltaVee47

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I am nearly finished with the FF kit so you might think I should be long over this but my frustration with nuplates just boiled over today. What am I missing here? It?s nearly impossible to get the very soft headed AN screws to screw into the nutplates without stripping. Why is this so hard? Is there a technique for this that I am missing? Grrrrr! I need a Tylenol.
Thanks for listening
Greg Beckner
N557GB
140366
 
I am nearly finished with the FF kit so you might think I should be long over this but my frustration with nuplates just boiled over today. What am I missing here? It?s nearly impossible to get the very soft headed AN screws to screw into the nutplates without stripping. Why is this so hard? Is there a technique for this that I am missing? Grrrrr! I need a Tylenol.
Thanks for listening
Greg Beckner
N557GB
140366

Run a tap through the nutplate after installation.

Depending on your riveting technique, sometimes the alignment with the hole can be slightly off, resulting in interference at the nominal thread axis. There can also be some manufacturing variability of the nutplates themselves, but all the ones I received from Van's recently have had smooth action.
 
One technique is to run an appropriate sized tap down into the nutplate. Of course that does reduce some of the effectiveness of the nutplate. In the RV-7 instructions Vans mentions this technique. If my memory is correct it is mentioned when installing the nutplates for the seat panels.

Another technique is putting a little oil on the screw threads and running it down with an electric screwdriver/drill and backing it out. I have also found that sometimes the nutplate is not fully aligned with the hole in the sheet metal and the screw is binding on the sheet metal. A small jeweler file can fix this issue.

I'm sure you will get other suggestions as well.
 
As suggested above, Boelube is a good answer.

Defeating the locking feature of the nutplates by running a tap through them defeats the designer’s purpose in putting a locking nutplate there. In some cases, this is OK - but only in some cases. If you do it indiscriminately, without understanding how aircraft are designed, you’re really butchering the project.
 
Another thing is that you must increase the downward pressure on the screwdriver proportionately as the resistence to turning increases. I learned some years ago to use a phillips bit on a ratchet for loosening really tight phillips screws. It makes it much eaier to get enough downward force, as you are using one hand to push down and another to turn. You might try that when tightening the first screw in a nut plate.

Larry
 
Defeating the locking feature of the nutplates by running a tap through them defeats the designer?s purpose in putting a locking nutplate there. In some cases, this is OK - but only in some cases. If you do it indiscriminately, without understanding how aircraft are designed, you?re really butchering the project.

Nutplates are not normally used for joints that require the full bolt strength. They do not perform as well as a regular nut whose threads come up to the material. An easy way to tell is if the bolt isn't torqued to spec, as is the case with all phillips head screws holding panels and such. These are what the OP was having trouble with, if I understood well.

It's not the locking of the nutplate that keeps the bolt from turning, that's normally only a small part of the total friction. The locking action can slow down nuisance unscrewing if the assembly wants to vibrate loose, and only after the nominal clamping friction has been defeated. A better way to accomplish the same is with loctite, for instance on the spinner and other highly cycled places.

Lubrication doesn't help if there is physical interference between the misaligned hole and the bolt. A thou of misalignment is practically impossible to see, but will greatly increase friction and cause galling and stripping. Running a tap takes care of this and doesn't damage the nutplate.

It is safe to run a tap through almost all nutplates.
 
Nutplates are not normally used for joints that require the full bolt strength. They do not perform as well as a regular nut whose threads come up to the material. An easy way to tell is if the bolt isn't torqued to spec, as is the case with all phillips head screws holding panels and such. These are what the OP was having trouble with, if I understood well.

It's not the locking of the nutplate that keeps the bolt from turning, that's normally only a small part of the total friction. The locking action can slow down nuisance unscrewing if the assembly wants to vibrate loose, and only after the nominal clamping friction has been defeated. A better way to accomplish the same is with loctite, for instance on the spinner and other highly cycled places.

Lubrication doesn't help if there is physical interference between the misaligned hole and the bolt. A thou of misalignment is practically impossible to see, but will greatly increase friction and cause galling and stripping. Running a tap takes care of this and doesn't damage the nutplate.

It is safe to run a tap through almost all nutplates.

Actually, the reason a nut-plate has a deformed thread is to prevent the bolt from backing out due to vibration in parts that, by design, can not achieve proper thread pre-load. For example when attaching fiberglass or thin sheet metal, where torqueing to spec will likely crack or deform the part. It has nothing at all to do with the joint strength. Running a tap through it damages the nut plate's locking feature. Do you really want to use loctite on every screw every time you take off your wheel pants? Lubrication absolutely reduces the running friction.
 
A better way to accomplish the same is with loctite, for instance on the spinner and other highly cycled places.

It is safe to run a tap through almost all nutplates.

I am certainly not an expert on any of this but I would just like to pass on my experience.

Over the last 3 years the screws on the spinner have gotten worse about being loose after every flight. At first it was just one or two. Lately almost every screw in the forward ring were loose after every flt. I tried loctite to no avail. It did help at first but then they still came loose. We just did the annual insp and I replaced all 12 nut plates in that ring. 12 hours and five flights later and they are all still tight.

Some of the screws in the seat pan were very tight so I tried the Boelube trick. That worked for most of them but some were still tight. I ran a tap thru them and that made it much easier. None of the seat pan screws come loose from one year to the next.

I would have to say that this statement is correct:

"Defeating the locking feature of the nutplates by running a tap through them defeats the designer?s purpose in putting a locking nutplate there. In some cases, this is OK - but only in some cases. If you do it indiscriminately, without understanding how aircraft are designed, you?re really butchering the project." - Ironflight

Remember that you are going to be the experimental test pilot every time you fly.
 
Video

Don't know if it helps, but about two weeks ago I made a video of how I install nut plates. What helps me (my tip) is cutting off a screw that is used to install the nutplate. This helps insure that it is in line with the parts once riveted which helps avoid binding from mis alignment. I also use boelube on the new full length screw at final assembly.

https://youtu.be/X6mvsGOSICU

Jim
 
There is a lot of talk about nutplate hole misalignment . I built my first two planes using the nutplate itself as a hole template. It certainly does work but takes a bit of extra time to get all the holes done. Most of the nutplate holes are already drilled on the RV14. On my third and subsequent planes I used a nutplate jig. It is the bomb. Much faster and very accurate.
As for the tapping vs not tapping, there is not a real hard and fast rule. Yes of course it would be nice if all the nutplates were perfect but there are differences. Sometimes just half a turn with a tap will make the screw fit easily in and maintain the locking feature. Yes you should use some sort of lubricant, Bloelube is a good product.
There are some locations where the screws are never going to back out, for example inspection plates in floorboards. It is really nice to not have struggle with tight screws on inspection plates. However this is not a hard and fast rule. I certainly do not want external inspection plates to come loose.
Stainless steel screws have a machined thread and they tend to go in a lot easier. Again in structural areas this might not be advisable. I use quite a few stainless screws on the cowlings, internal inspection plates and to fasten floor boards down etc. Bloelube is still a good idea when using stainless but it is not typically necessary on subsequent insertions.
 
Over the last 3 years the screws on the spinner have gotten worse about being loose after every flight. At first it was just one or two. Lately almost every screw in the forward ring were loose after every flt. I tried loctite to no avail. It did help at first but then they still came loose.

Spinner is indeed a special case, as those are the most highly stressed nutplated joints on the entire airplane!

Keep in mind that methacrylate-based threadlockers such as Loctite 242 do need contact with bare metal to cure properly. There are two simple ways to ensure this:

1. Do not reuse the bolt!

2. Run a tap through the nutplate to remove old Loctite and expose the metal.

I must have replaced my spinner at least eight times so far and never had a loose screw--every one gives a satisfying pop when first cracked loose.

Paradoxically, if you must reuse the fastener it is better to simply leave old Loctite on there. Re-applying fresh Loctite when there is no contact with metal results in it not curing properly, and might even act as lubricant to hasten the undoing of the joint. Lots of good info from the experts.

Then, there are different sizes of taps. If you are worried about loss of locking action it is best to buy a "close fit" tap from a proper machinist supply. These are 3-6 thou tighter than hardware-store variety. See here for example.


Good advice from BillL mentioning ACR Ribbed phillips inserts. I've had good luck with these from Brown Tool. They only work for removal though.
 
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Nutplates are not normally used for joints that require the full bolt strength. They do not perform as well as a regular nut whose threads come up to the material. An easy way to tell is if the bolt isn't torqued to spec, as is the case with all phillips head screws holding panels and such. These are what the OP was having trouble with, if I understood well.

It's not the locking of the nutplate that keeps the bolt from turning, that's normally only a small part of the total friction. The locking action can slow down nuisance unscrewing if the assembly wants to vibrate loose, and only after the nominal clamping friction has been defeated. A better way to accomplish the same is with loctite, for instance on the spinner and other highly cycled places.

Lubrication doesn't help if there is physical interference between the misaligned hole and the bolt. A thou of misalignment is practically impossible to see, but will greatly increase friction and cause galling and stripping. Running a tap takes care of this and doesn't damage the nutplate.

It is safe to run a tap through almost all nutplates.

The above is contrary to the process specifications of the large aerospace company I work for.

There are many, many varieties of self locking nutplates and many of them share the properties of, and are direct replacements for nuts in both tension and shear applications.

The free running torque is the "locking feature" of the fastener. Once that running torque is no longer meeting specification the nutplate is junk. Most nutplates are expected to last 5 cycles and still meet spec. There are also "long life" nutplates that can go longer in field service. Of course we are not held to this standard with E-AB, but aircraft OEM's take this stuff seriously. We replace low running torque nutplates by the hundreds when our airplanes return to the depot.

If one has physical interference due to misallignment, the nutplate is installed wrong. Simple as that.

Running a tap through a nutplate removes material from the mechanically distorted portion and eliminates the self locking function as well as weakening the fastener itself. There are circumstances where this is acceptable, but saying this situation is categorically "safe" for almost all nutplates is incorrect.
 
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The above is contrary to the process specifications of the large aerospace company I work for.
There are many, many varieties of self locking nutplates and many of them share the properties of, and are direct replacements for nuts in both tension and shear applications.
The free running torque is the "locking feature" of the fastener. Once that running torque is no longer meeting specification the nutplate is junk. Most nutplates are expected to last 5 cycles and still meet spec. There are also "long life" nutplates that can go longer in field service. Of course we are not held to this standard with E-AB, but aircraft OEM's take this stuff seriously. We replace low running torque nutplates by the hundreds when our airplanes return to the depot.
If one has physical interference due to misallignment, the nutplate is installed wrong. Simple as that.
Running a tap through a nutplate removes material from the mechanically distorted portion and eliminates the self locking function as well as weakening the fastener itself. There are circumstances where this is acceptable, but saying this situation is categorically "safe" for almost all nutplates is incorrect.

Very well stated. Please listen to what Michael says. Platenuts are designed the way they are on purpose. Don't destroy that purpose.
Personally I use the "wax" lube method for initial threading into a new platenut. A toilet bowl wax seal ring is cheap, works great, and lasts a long time.
 
There are many, many varieties of self locking nutplates and many of them share the properties of, and are direct replacements for nuts in both tension and shear applications.

I don't doubt that this is true, but our run-of-the-mill K1000-08 nutplates almost certainly don't fall into this category. It's good that you called me on it as I went to find the tensile/shear spec for these and can't seem to dig up an authoritative source. Perhaps someone can link if you know of one? Some vendor sites list 700 lbs yield spec for the -3 size, which is significantly lower than ~2000 lbs for a regular AN3 assembly, as I would expect just from looking at the fragile little thing.

The free running torque is the "locking feature" of the fastener. Once that running torque is no longer meeting specification the nutplate is junk. Most nutplates are expected to last 5 cycles and still meet spec. There are also "long life" nutplates that can go longer in field service. Of course we are not held to this standard with E-AB, but aircraft OEM's take this stuff seriously. We replace low running torque nutplates by the hundreds when our airplanes return to the depot.

I hear ya. The reality is that keeping to that spec would make almost every E-AB in existence non-airworthy, at least among the ones I've been around so far!

If one has physical interference due to misallignment, the nutplate is installed wrong. Simple as that.

Agreed. Again, this is a fairly common occurrence in amateur hands.

Running a tap through a nutplate removes material from the mechanically distorted portion and eliminates the self locking function as well as weakening the fastener itself. There are circumstances where this is acceptable, but saying this situation is categorically "safe" for almost all nutplates is incorrect.

Well, the only categorically true statement is that any advice you read on teh internetz is worth exactly what you paid for it. :p

I see that our little "run a tap through it" camp has polarized the discussion, but the result has been very educational so let's leave the discussion here for posterity.

FWIW, I posit that lubricating the fastener also reduces the locking function, perhaps in an even worse way than mild re-cutting, as the re-cutting won't remove all locking--the nut will expand around the tap.
 
So the running-a-tap-though debate aside, if you are stripping the drive heads, that is another long running issue. Just use drive bits, preferably an ACR bit. I found (finally) screw drivers typically are highly inferior to the driver bits (except the $$$$ ones). I only use the bits now and seldom strip a head, and never on the first use. Do a search on VAF and several threads will come up.

......

I found that replacing the usual AN515 screws that are rated at 60K psi tensile with more structural screws, such as these at 125K psi - I like the washer head look inside the cockpit for floor/bulkhead attach -

https://www.aircraftspruce.com/catalog/hapages/an525.php

Or these at 160K psi tensile - normal head shape -

https://www.aircraftspruce.com/catalog/hapages/nas600.php

Or even these if the hex head helps access, at 160k psi - really helped in a few spots on the -6A on the floor stiffeners and firewall -

https://www.aircraftspruce.com/catalog/hapages/nas1801.php

Or these at 125K psi, but you have to allow for grip length -

https://www.aircraftspruce.com/catalog/hapages/ms27039.php

All of the above are made from a stronger steel and seem to last longer and get less bugg**ed up with philips head screwdrivers. :)

PS also use Boelube for the first insertion and I have never run a tap through a nutplate. :)
 
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I hear ya. The reality is that keeping to that spec would make almost every E-AB in existence non-airworthy, at least among the ones I've been around so far!

So..... that is an indication to me that entirely too many nut-plates are being tapped.

During my build, I tapped exactly...zero. It is not needed. Use of good installation technique and proper tools address most. A little whale oil (Boelube) or wax fixes the few tight ones.
 
Do you really want to use loctite on every screw every time you take off your wheel pants?

Absolutely! If there is any doubt whether it wants to move, I glue it. And throw away used fasteners too--remember the tragedy at Reno. It's really not that much of a hassle, trace amounts will do the work if applied properly. I figure, if the method works well on the spinner it will work most everywhere else. YMMV
 
So..... that is an indication to me that entirely too many nut-plates are being tapped.

During my build, I tapped exactly...zero. It is not needed. Use of good installation technique and proper tools address most. A little whale oil (Boelube) or wax fixes the few tight ones.

I think you misunderstood my meaning: I tapped fewer than a dozen nutplates on my two builds, and those mostly for convenience--I'm quite careful with installation and will redo if it's not smooth.

On the other hand, the plate cover over my instrument panel must have come off at least fifty times for tinkering. If you do proper annuals you'd have to replace most of the nutplates on the airplane in year six per Toolbuilder's spec!
 
Mr. Aluminum, You are free to do whatever you are comfortable with on your aircraft. It is indeed experimental. But you seem to be indicating that tapping platenuts is common practice. In your corner of the world, it may be. But I have and continue to inspect hundreds of amateur-built aircraft every day, and I have NOT found this practice to be the "standard".

To others, Please don't follow "non-standard aircraft practices" without at least consulting with Certified Aircraft Mechanics (A&Ps) or EAA Technical Counselors.
 
Gil got it right in post #20. Generally speaking the stronger screws perform a lot better.

One thing that some unwary people might think, is that if they are drilling all the holes they can downsize the screw diameter because it's a stronger material. Not so - often its the strength of the hole or nutplate or some factor that governs. But merely replacing a weaker screw with a similar stronger one, that's fine.

Dave
Old Engineer
RV-3B building
 
... If you do proper annuals you'd have to replace most of the nutplates on the airplane in year six per Toolbuilder's spec!

It's not "my" spec, it is found in the data sheets of the manufacturer. And yes, nutplates do "wear out" in use. The fasteners securing inspection panels in front of the inlets of the jet engine are checked for running torque at EVERY installation, for example.
 
+1 for a touch of Beeswax

I have a small cake of beeswax purchased from the local JoAnn's Fabric store.


I scrape the end few threads of each screw against the cake before the first use of the nutplate. After the first use no further use of wax is required, even for fresh screws. Screws run in smooth and easy. I also toss any screw with less than a perfect head, and any driver bit that does not have crisp sharp edges.


I run the screws in with a driver till snug, and finish tightening with a hand driver.

Never broke a screw when doing this, and I don't have the mess of Boelube liquid to deal with.
 
Nutplate

Thanks to everyone for the great ideas. I especially like Gil?s idea in post #20. My BMW motorcycle is built with star screws which never strip.
Last question (for now). How is running a tap through the lock ring of the nutplate different from forcing the designated screw through the lock ring? When I fit the snorkel I must have run the screws through the nutplates around the filter ramp at least 15 times before I got everything just right. Does this mean that those nutplates are shot and I should replace them?
Greg
N557GB
 
Last question (for now). How is running a tap through the lock ring of the nutplate different from forcing the designated screw through the lock ring?
N557GB

No lock ring like a nylon lock nut. The nut plate is mechanically deformed (i.e. squished on two sides) after being tapped, creating at bit of an oval shape. As the screw goes in, it force the sides of the oval back into a circle. However, it is a spring action, due to it' limited movement and steel type, and comes back to oval again when the screw is removed. This spring tension is what "locks" the threads.

Tapping re-cuts the threads to be perfectly round again and therefore no tension and no locking. However the sharp teeth of the tap cut into the steel instead of forcing it to expand from oval to round. Also, the deeper threads cut into the sides of the oval also takes away from the structural metal, weakening the nutplate.

The first screw in has more friction due to the rough thread finish from the plating/painting. The first screw in will burnish/clean up the plate nut's threads so that future screws go in much easier.

Larry
 
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Thanks to everyone for the great ideas. I especially like Gil’s idea in post #20. ...

Last question (for now). How is running a tap through the lock ring of the nutplate different from forcing the designated screw through the lock ring?
....
Greg
N557GB

Simpler answer - the tap has a cutting edge and removes material, the screws do not. :)
 
Well, I guess I will jump back in to the conversation. Please review page 8-5 of the Vans RV-7 build manual where they state "it is acceptable to run an 8-32 tap through the nutplates." This is in reference to the seat pans and the outer ribs.

They do not say to do it indiscriminately and neither did I.

Have fun with the conversation.
 
***Sigh***

I think I've seen this discussion come up at least once every year, and the same fighting camps emerge. Its almost a religious argument with all kinds of half truths and hard over suppositions. IMHO, one needs to evaluate where the nut plate is going and what its expected purpose is, and indeed they have two purposes - to act as a nut where access to said nut not simple or desired, and/or to act as a locking nut where said nut etc....

I run a tap thru my nutplates when I'm going to be doing a lot of screw insertion and removal of said part - which when you are ex-peri-ment-ing, that happens alot. If I need that plate in the final insertion, and forever more to be a locker, then it either gets replaced, or much more likely, the screw gets safety wired, or Locktited or the nutplate gets re-squeezed. OMG - Resqueezed! Imagine that.

Theres more than one correct way to skin this cat, and its application specific. One would think with the proper application of common engineering sense, we could all at least agree on that.
 
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Theres more than correct way to skin this cat, and its application specific. One would think with the proper application of common engineering sense, we could all at least agree on that.

In keeping with Maniago's post about alternatives:

Instead of tapping, I used a different type of aviation #8 screw in the problem areas (not just the pan edges but anywhere using a Phillips would be a pain. With these 'drop in replacement' hex heads, they are a breeze to install/remove without killing yourself with effort to keep the Phillips engaged. (READ: It makes electric screwdriver work for real. EVERYWHERE)

Here is a Spruce Link:
NAS1801-08-07 Hex head screws

I think these things are wonderful.
 
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Chapsticks work great for lubricating screws and I used cap screws w
Every place i could.

I think the only place that has 8-32 pan head screws is under the seat cushions; however, along the sides of the seat pans are cap screws.
 
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